1. Field
The presently disclosed embodiments relate generally to apparatus, methods and systems for generating x-rays using field emission technologies and the use thereof, principally in the area of brachytherapy.
2. Technical Background
Since the discovery of the x-rays by William Roentgen in 1895, practically all man-made x-ray generators have been built around the same basic design. This design comprises a tube housing two spatially separated electrodes (an anode and a cathode), a high voltage generator supplying voltage between the electrodes to create an accelerating electric field therebetween, and a means to create an electron beam directed from the cathode to the anode. In operation, electrons leave the cathode, are accelerated by the electric field, and impinge on the anode. As the electrons decelerate at the anode surface their kinetic energy in part is released in the form of an emission of x-rays.
A principle difference in the various such man-made x-ray generators is in the method of creating the electron beam. Basically, these methods include the use of a thermionic cathode to generate the electron beam or the use of an electron field emission effect. Each of these methods of x-ray production relies upon different technologies and different physical processes. Consequently, each method requires different hardware in implementing a particular method of x-ray production and use, with one methodology not necessarily being able to use the hardware of the other methodology.
X-rays produced with a thermionic cathode utilize a cathode heated to a temperature sufficient to cause electrons to “boil” off the cathode. The electrons are then pulled by an applied electric field to an anode. Upon striking the anode, a small portion of the electrons' kinetic energy is converted into x-rays, with the remainder being converted to heat. For this reason, most such x-ray devices utilize a rotating anode so that the heat is evenly spread over the anode.
As noted, x-rays can also be produced using field emission technology. Apparatus producing x-rays by field emission include a cathode and an anode held in a vacuum and the application of a high voltage electric field between them. The electric field pulls electrons from the cathode and accelerates them toward the anode with a kinetic energy dependent upon the electric field strength. Upon striking the anode, the electrons release some of their kinetic energy in the form of x-rays. The larger the operating voltage between the anode and cathode, the greater the energy that the produced x-rays will have.
The use of x-rays for therapeutic uses has been widely adopted. These therapeutic uses include, but are not limited to radiation therapy as a treatment for various forms of cancer. In addition, radiation therapy has been proposed for a form of a progressively degenerative eye disease known as macular degeneration.
Overview
Disclosed herein is an x-ray field emission apparatus, system and method, wherein the apparatus comprises a hollow probe held at vacuum; a cathode enclosed within the probe, wherein the cathode produces an electron stream when connected to a high voltage generator; an anode enclosed within the probe and separated from the cathode by a gap, wherein anode provides a target for the electron stream; and a shield assembly comprising a hollow shield electrode positioned within the probe and about the cathode.
Also disclosed herein is an x-ray field emission apparatus comprising a housing having proximal and distal housing ends; a hollow, substantially cylindrical probe having proximal and distal probe ends, the housing and probe being attached to each other and forming a single vacuum chamber; a cathode having proximal and distal ends disposed within the apparatus and longitudinally movable with respect thereto, the cathode producing an electron beam directed towards the distal probe end when connected to a high voltage negative potential; an anode disposed within the probe at the distal probe end, the anode and cathode separated by a gap; and a shield assembly comprising a hollow shield electrode positioned within the probe and about the cathode.
Further disclosed herein is an x-ray field emission apparatus comprising a housing having proximal and distal housing ends; a hollow, substantially cylindrical probe having proximal and distal probe ends, the housing and probe attached to each other and forming a single vacuum chamber; a cathode having proximal and distal ends disposed within the apparatus and longitudinally movable with respect thereto, the cathode producing an electron beam directed towards the distal probe end when connected to a high voltage negative potential, the cathode being made of a soft ferromagnetic material; an anode disposed within the probe at the distal probe end, the anode and cathode separated by a gap; and a shield assembly comprising a hollow shield electrode positioned within the probe and about the cathode.
An x-ray field emission apparatus comprising a housing having proximal and distal housing ends; a hollow, substantially cylindrical probe having proximal and distal probe ends, the housing and probe attached to each other and forming a single vacuum chamber; a cathode having proximal and distal ends disposed within the apparatus and longitudinally movable with respect thereto, the cathode producing an electron beam directed towards the distal probe end when connected to a high voltage negative potential, the cathode being made of a permanently magnetized hard ferromagnetic material; an anode disposed within the probe at the distal probe end, the anode and cathode separated by a gap; and a shield assembly comprising a hollow shield electrode positioned within the probe and about the cathode.
Also disclosed is a method of operating an x-ray field emission apparatus comprising providing an x-ray field emission apparatus comprising a housing having proximal and distal housing ends; a hollow, substantially cylindrical probe having proximal and distal probe ends, the housing and probe attached to each other and forming a single vacuum chamber; a cathode having proximal and distal ends disposed within the apparatus and longitudinally movable with respect thereto, the cathode producing an electron beam directed towards the distal probe end when connected to a high voltage negative potential; an anode disposed within the probe at the distal probe end, the anode and cathode separated by a gap; and a shield assembly comprising a hollow shield electrode positioned within the probe and about the cathode; and moving the cathode relative to the shield assembly to vary the current output of the anode.
A further disclosure included herein is of an x-ray field emission apparatus comprising: a housing having proximal and distal housing ends; a hollow, substantially cylindrical probe having proximal and distal probe ends, the housing and probe attached to each other; a cathode having proximal and distal ends disposed within the apparatus, the cathode producing an electron beam directed towards the distal probe end when connected to a high voltage negative potential; an anode disposed within the probe at the distal probe end, the anode and cathode separated by a gap; and a magnetic focuser for steering the electron beam towards the anode.
Further disclosed herein is an x-ray field emission apparatus comprising: a housing having proximal and distal housing ends; a hollow, substantially cylindrical probe having proximal and distal probe ends, the housing and probe attached to each other; a cathode having proximal and distal ends disposed within the apparatus, the cathode producing an electron beam directed towards the distal probe end when connected to a high voltage negative potential; an anode disposed within the probe at the distal probe end, the anode and cathode separated by a gap; a shield assembly comprising a hollow shield electrode positioned within the probe and about the cathode; a cathode high voltage generator electrically connected to the cathode; and a shield assembly high voltage generator electrically connected to the shield assembly; wherein the an electromstatic focuser comprises a shield assembly operated at a higher negative potential than the cathode.
Also disclosed herein is an x-ray field emission apparatus comprising: a hollow probe held at vacuum; a cathode enclosed within the probe, the cathode producing an electron stream when connected to a high voltage generator, the cathode having proximal and distal cathode ends; an anode enclosed within the probe and separated from the cathode by a gap, the anode providing a target for the electron stream; and a field emission element disposed at the distal cathode end wherein the field emission element is made of a composite material comprising carbon fibers embedded in a conductive binder.